Here is the link for turning on less secure apps for Regular Gmail accounts https://myaccount.google.com/lesssecureappsIn addition to allowing Less Secure apps, you will have to ensure Two Step Verification is turned OFF

If you are the administrator of your GSuite account it may require you to visit the link in the screenshot below (Learn how to control access to less secure apps). You can access that link by clicking the link here https://support.google.com/a/answer/6260879

2. Click on the user/admin you are using to login3. Click on security4. Once you're there click: “Turn off identity questions for 10 minutes after a suspicious attempt to sign in”5. Now save your campaign configuration in Dubb again and you should have access